FIG. 4 is a block diagram of a conventional phase measuring circuit of a phased array antenna disclosed in Japanese Published Patent Application No. 55-170159, and FIG. 5 is a block diagram showing a conventional phase measuring circuit of a phased array antenna having both functions of transmission and reception. In FIGS. 4 and 5, reference numeral 1i (i=1 to n) designates an element antenna. A phase shifter for reception 2i (i=1 to n) shifts the phase of the signal received by the element antenna 1i. A phase shifter for transmission 3i (i=1 to n) shifts the phase of the signal transmitted by the element antenna 1i. A control circuit 4 controls the phase of the phase shifters 2i and 3i. A combiner circuit 5 combines the signal received by the element antenna 1i. Reference numeral 7 designates a terminal for the received signal. A phased array antenna 9 of FIG. 4 comprises the element antenna 1i, the phase shifter for reception 2i, the control circuit 4, the combiner circuit 5, and the terminal 7. A test antenna 10 transmits and receives a test signal so as to measure the phase of the phased array antenna 9. A signal generator 11 generates a test signal to be applied to the test antenna 10a. A receiver 12 receives the test signal which is received by the test antenna 10b, where the received test signal is a signal resulting from that the test signal is transmitted from the phased array antenna 9.
The operation of the apparatus of FIG. 4 will be described with reference to FIG. 4. Combined electric field vector is represented by a vector sum of electric field vectors of the respective element antennas 1i while the whole arrays in the phased array antenna operate. Supposed the electric field vector of the `i`th element antenna 1i be Ei exp(j.phi..sub.i) where Ei is amplitude, .phi..sub.i is phase, j is imaginary unit, the combined electric field vector obtained when the phase of the `i`th element antenna 1i is shifted by degree is represented as follows; EQU E.sub.1 =E.sub.0 exp (j.phi..sub.0)-Ei exp(j.phi..sub.i)(1-exp(j.DELTA.)) (1)
The above equation (1) is transformed to; EQU .vertline.E.sub.1 .vertline..sup.2 /E.sub.0.sup.2 =(Y.sup.2 +K.sup.2)+2YKCcos (.DELTA.+.DELTA..sub.0) (2)
where EQU Y.sup.2 =(cosX-K).sup.2 +sin.sup.2 X (3) EQU tan .DELTA..sub.0 =sinX/(cosX-K) (4) EQU K=En/E.sub.0 (relative amplitude) (5) EQU X=.phi..sub.i -.phi..sub.0 (relative phase) (6)
Supposed the ratio of the maximum to the minimum of the equation (2) be r.sup.2, the following equation is obtained. EQU r.sup.2 =(Y+K).sup.2 /(Y-K).sup.2 ( 7)
In addition, from the equation (2), -.DELTA..sub.0 is a phase change which provides the maximum value of .vertline.E.sub.1 .vertline..sup.2 /Eo.sup.2, namely, the relative electric power, and these r and .DELTA..sub.0 are obtained from the measurement of the relative electric power of the equation (2).
More specifically, in case of the phased array antenna for reception, a signal from the signal generator 11 is transmitted from the test antenna 10 and the signal is received by the `i`th element antenna 1i. The signal received by the `i`th element antenna 1i is shifted in its phase by the phase shifter 2i under the control by the control circuit 4. The signals received by the respective element antennas 1i are combined by the combiner circuit 5. Then, the ratio r of the maximum to the minimum of the signal from the receiving signal terminal 7 and the phase quantity .DELTA..sub.0 attaining the maximum value are measured. By employing the equations (1) to (7) using these values, a relative amplitude and a relative phase of the `i`th element antenna 1i can be obtained. By conducting this measurement and this calculation for all element antennas 1i (i=1 to n), the relative amplitude and the relative phase of the respective element antennas 1i (i=1 to n) can be obtained.
FIG. 5 shows a conventional phase measuring circuit of a phased array antenna having transmitting and receiving functions. The circuit of FIG. 5 includes, in addition to the elements of the phase measuring circuit having only a receiving function shown in FIG. 4, a divider circuit 6 for dividing the transmitted signal to the element antenna 1i, a terminal for a transmitted signal 8, and phase shifters for transmission 3i (i=1 to n).
In this phased array antenna 9b, the signal from the signal terminal 8 is divided by the divider circuit 6 and the phase of the divided signal is respectively shifted by the phase shifter for transmission 3i under the control by the control circuit 4. The phase-shifted signal is then excited by the element antenna 1i and emitted into the space. The signal radiated from the respective element antennas 1i is received by the test antenna 10b and the received signal is received and processed by the receiver for test 12. The ratio r of the maximum to the minimum of the signal change of the received signal and the phase quantity .DELTA..sub.0 for attaining the maximum value are measured and the equations (1) to (7) are operated to obtain the relative amplitude and the relative phase of the `i`th element antenna 1i in the transmission system. By performing measurement and calculation for all element antennas, the relative amplitude and the relative phase of respective element antennas 1i (i=1 to n) can be obtained.
FIG. 6 is a block diagram showing a conventional antenna diagnosis apparatus disclosed in Japanese Published Patent Publication No. 57-162803, in which the phase and the amplitude of the element antenna are set and processed by the measuring and operating circuit and the diagnosis circuit. Referring to FIG. 6, reference numeral 101 designates an element antenna. A phase shifter 102 shifts the phase of the transmission signal to be transmitted from the element antenna 101. A divider circuit 103 divides the transmission signal to the element antenna 101. Reference numerals 104 and 108 designate transmission sources. An antenna 109 is confronted to element antennas 1i. A control circuit 111 controls the phase shifter 102. A measuring and operating circuit 112 measures the level change of the combined and received signal output of the whole element antennas and operating the amplitude and the phase of each element antenna. A diagnosis circuit 113 compares its measured and operated result with a reference value to diagnose the measured result. A switch 110 selects one from a state where the signal from the transmission source 104 is applied to the array antenna or the signal received by the respective antenna 101 which is transmitted from the confronting antenna 109 is supplied, to the control circuit 111.
The operation will be described with reference to FIG. 6. When the amplitude and the phase of each element antenna 101 is diagnosed during the whole array operate, the switch 110 is switched to the side of the control circuit 111 and, at the same time, the transmission source 108 is operated, whereby the electric wave is transmitted from the confronting antenna 109. Then, on the bases of the same measuring theory as performed in the apparatus shown in FIGS. 4 and 5, the phase of the signal of each element antenna 101 is shifted by the phase shifter 102 under the control by the control circuit 111, the change in the combined output level of the whole array is measured by the measuring and operating circuit 112, then the amplitude and the phase of each element antenna 101 are calculated, and the results are transmitted to the diagnosis circuit 113. In the diagnosis circuit 113, the amplitude and the phase value of each element antenna which are measured and calculated after receiving the electric wave from the confronting antenna 109 at the start of operation of the phased array antenna with setting the conditions, such as set phase, frequency, and polarization of each element antenna 101, and the set position of the confronting antenna 109 at the same, are stored. Thus, the above-described measured results are compared with the data of reference amplitude and reference phase at the start of operation, and when the result of this diagnosing shows that the phase is shifted as compared with the reference phase, the control of the corresponding phase shifter is changed so as to correct the phase of the element which is shifted with relative to the reference.
In the conventional phase measurement circuit of a phased array antenna having such a structure, it is necessary to provide measuring circuits of transmission and reception systems separately in a phase measuring circuit of the phased array antenna having transmitting and receiving functions for such as satellite communication, and this makes the apparatus large in size and the control by the control circuit complicated. Further, when a phase measuring circuit is incorporated in the phased array antenna as a failure diagnosis circuit, its structure is particularly complicated.